The SBS modified asphalt was modified by both rubber powder and high viscosityagent.The preparation process of high viscosity modified asphalt was studied by basic phys-ical indexes.The thermal storage stability of high viscosity modified asphalt was studied bythe softening point difference method.High temperature rheological properties and mediumtemperature anti-fatigue of high viscosity modified asphalt were studied by DynamicS hearRheological(DSR) test.The modification mechanism of high viscosity modified asphalt wasanalyzed by Fourier Transform Infra-Red(FTIR) and Differential Scanning Calorimetry(DSC) .The results of basic physical experiments show that rubber powder can improve thehigh temperature performance of modified asphalt， but it has adverse effect on its low tem-perature performance.High viscosity agent can greatly improve the viscosity of modifiedasphalt.The optimum contents of rubber powder and three kinds of high viscosity agentsare 10%， 8%， 7%and 8%respectively.The results of segregation test show that the the r-mal storage stability of three kinds of high viscosity modified asphalt meets the require-ments of the specification.DSR testresults show that rubber powder and high viscosity a-gent can improve the high temperature performance and temperature sensitivity of the SBSasphalt.After short-term aging， the high temperature performance of SBS asphalt is im-proved， but it has adverse effect on temperature sensitivity.The addition of rubber powderand high viscosity agent improves the medium temperature anti-fatigue of asphalt.FTIR re-sults show that there are physical blending and chemical reaction between rubber powder，high viscosity agent and SBS asphalt.DSC results show that the high temperature stabilityof asphalt is improved effectively through high viscosity composite modification.